How did the lives of native americans change in the new world because of the colombian exchange?

The Columbian exchange caused Native Americans to come into contact with diseases like small pox, yellow fever, and malaria. Since they had not developed resistance to these types of illnesses, a lot of them died from it.

The deaths of all of these Native Americans caused for a labor shortage, which eventually lead to African slavery, since most of the Natives had died off.

the answer is prolly b

the perimeter of a triangle is 69 cm. side a is 5 cm shorter than side b. side c is twice as long as side a. find the length of each side. i need to know how to do it in 2 equations.  

equations:

a = b-5

c = 2a

a + b + c = 69